Electromagnetic translating device



Sept. 17, 1929. B. F. MIESSNER ELECTROMAGNETIC TRANSLATING DEVICE Filed June 8, 1927 INVENTOR fif/wA/m/v Mass/v51? ATTORNEY Patented Sept. 17, 1929 BENJAMIN F. MIESSNER, OF SOUTH ORANGE, NEW JERSEY ELECTROMAGNETIC TRANSLATING DEVICE Application filed June a,

My invention relates generally to an electro-magnetie translating device, and is particularly adapted to the function of translating sound-representing mechanical motion 5 into sound-representing electrical motion, and vice versa, in phonographic reproduction and recording.

It has for a particular object the arrangement of such a device in a simple way readily 10 adapted for association with existing phonographs, vacuum tube amplifiers and loud speakers, and atthe same time adapted for good quality reproduction or recording and efficient operation. Other objects will fol- 15 low from the accompanying description and drawings.

Fig. 1 shows the translating device in elevation'i- Fig. 2 is an end View of Fig. 1 looking from the bottom. Fig. 3 shows in detail one of the features of the device. Fig. 4- shows in diagrammatic form the association of the device with a phonographic record, vacuum tube amplifier and loud speaker.

Fig. 5 shows a simple way of mounting the 25 device for use with a phonograph. Like reference numerals in the several figures represent like parts.

Referring to Fig. 1, the element 1 is a permanent magnet of horseshoe or other suitable form having two pole pieces 2, preferably shaped and associated somewhat as shown in Figs. 1 and 2, suitably secured to magnet 1 as by screws 3. A core 4 of magnetic ma terial is formed with the magnet 1, or secured thereto by a screw 5, to project towards and in line with the gap between pole pieces 2. An armature 6 of magnetic material is flexibly attached to core 4 by a flexible strip 7 of steel or like magnetic material as shown in detail in Figs. 1 and 3, which show a relatively high degree of flexibility of the strip compared to the armature, the core 4 and the armature 6 being suitably split or slotted to receive the strip 7, good magnetic contact being forced in both instances by holding screws 8 and 9. The core 4 and armature 6 are shaped at 10 to permit of relative movement, but to form a short air gap of large area to permit of passage of magnetic flux in addition to the magnetic path by way of the 1927. Serial No. 197,316.

flexible strip 7. The armature 6 passes through the air gap between pole pieces 2, and is centered therein by an elastic or resillent material, such as soft live rubber, and preferably in the manner shown by a band of such material entirely encircling the armature and of such dimensions as to nicely fill the gaps between the armature and pole pieces. The end of the armature extending beyond the gap is bored or otherwise fitted to receive a phonograph needle 11 for reproduction, or suitable cutting tool for recording, held in place as by a thumb screw 12. The armature is preferably provided with an extension 14, Fig. 3, for dynamic balancing of the weight of set screw 12 during the vibratory action of the armature.

A coil 15 of proper number of turns of wire for the range of frequencies to be covered by the translating device surrounds while permitting movement of armature 6, and is preferably located near the pole pieces 2, as by being set in a recess provided by shaping the pole pieces as illustrated, this coil having two terminal wires 16 and 17 for connection to suitable amplifying apparatus as shown in Fig. 4.

Fig. 4 shows the translating device associated with a revolvable phonograph-record 21, the coil 15 being connected to a 3-elcctr0de vacuum tube amplifier 19 (which may comprise several stages of amplification if desired) through a potentiometer 18 by which the volume of sound may be simply controlled without changing the adjustment of the amplifier, the loud speaker 20 or other sound producing device being operated by the output energy of the amplifier. It is of course understood that the system of Fig. 4, which is for reproduction, is reversible for record mg.

Fig. 5 shows the translating device suitably enclosed in a casing 21 carried by an arm 22 universally pivoted at 24 to a stand 23 of suflicient weight to support the device and arm when lifted off the record. The stand may house the potentiometer 18 of Fig. 4, carry an external control knob 25 therefor, and be provided with a suitable flexible plug cord to the amplifier carrying connecting wires 26 and 27.

In operation the needle in the groove of the revolving record causes the armature 6 to move about the strip 7 as a pivot with respect to-the pole pieces 2 against the inertia of the device as a whole and the elasticity of the rubber band 13, thereby changing the length of the gaps between the pole pieces and the armature to alter the magnetic flow through the armature and induce corresponding current changes in the coil 15, and which changes are impressed upon the amplifier 19 in the manner shown in Fig. 4. The provided mounting of the armature permits reasonably free movement and provides for making the armature sufficiently short to facilitate a construction which is rugged and yet having a natural period sufficiently removed from the normal operating frequencies not to be troublesome. The centering of the armature in the gap with the simple encircling rubber band simplifies adjustment for such centering, which is quite important in such a device, and at the same time keeps foreign bodies, such as iron filings, out of the gap whose presence might interfere with operation. The rubber band also has the beneficial effect of damping the armature and rendering it aperiodic, and produces a restoring force that varies with displacement the reverse of the change in magnetic pull with displacement, a particularly desirable feature in recording or cutting of new records. The

location of the coil near the pole pieces reduces the effect of magnetic leakage from the armature and core to the main body of the magnet. Any leakage occurring above the coil is not a loss as far as the coil is concerned, as the magnetic lines involved in this leakage thread the coil.

Having described my invention, I claim:

1. In an electromagnetic phonograph pick-up device, the combination of a magnet having L-shape-d pole pieces spaced apart and shaped to form a flux concentrating air gap, a coil positioned within the angle of and supported by said pole pieces, a magnetic pro ection extending from said magnet towards said gap, an armature extending from said projection through said gap substantially parallel to the axis of said coil, and a flexible element of magnetic material linking said projection and armature, said projection and armature each having substantially more cross-sectional area than said flexible element and being so abutted as to have a short air gap therebetween of area larger than the crosssectional area of the one of said elements having the smaller said area, whereby the magnetic flux through said flexible element is materially supplemented.

2. In an electromagnetic phonograph pick up device the combination of a magnet having L-shaped pole pieces spaced apart to form tion and armature, said projection and arma-- ture each having substantially more crosssectional area than said linking element, and 1 being concavedly-convexedly abutted with a short air gap therebetween.

In testimony whereof I hereunto afiix my signature.

BENJAMIN F. MIESSNER. 

